1. Field of the Invention
This invention relates to an arrangement to allow a synchronized display of MAC (multiplexed analog component) signals on a television monitor which is designed to display standard video signals.
2. Description of the Prior Art
For a satellite transmission, a C-MAC system uses different modulation methods for the video signals as compared to the sound and data signals The digitally coded sound and data are broadcast as a 2-4 PSK signal and the MAC video signal is broadcast using normal frequency modulation. These two signals are time multiplexed after RF modulation. The MAC (multiplexed analog components) signal is a base-band time-multiplex signal of time compressed analog video components.
Conventional television monitors for monitoring television signals are designed to display a standard video signal such as shown in FIGS. 1a and 1b. Blanking intervals 2 between the actual pictures segments 1 occur during intervals when the picture signal is interrupted for the purpose of the return of the beam of the monitor. The signal level during the blanking interval has a predetermined constant level 3 which in most television systems corresponds to the black level of the picture signal. During the blanking interval, a line repetitive line synchronizing pulse 4 and a field repetitive field synchronizing pulse 5 are transmitted. In the monitor, a synchronizing pulse frame is created from the sequence of line and field synchronizing pulses so as to control the synchronization of the monitor. For synchronized display of the normal video signals at the correct brightness, the known monitors evaluate the synchronizing pulse frame and the black level 3 transmitted immediately after the synchronizing pulses 4.
For future satellite television transmission systems MAC signals (multiplexed analog components) such as shown in FIG. 2 will be used and there are various proposals for standards that exist. The C-MAC signal, for example, is described in the publication "Rundfunktechnische Mitteilungen" (Broadcasting reports) year 29 1985, Vol. 1, pages 23-35. The D2-MAC signal, for example, is described in "Specification du Systeme D2-MAC/Paquet" (specification of the D2-MAC/Paquet system) of September 1985 Telediffusion de France. Common to all of these different MAC signal systems, is that they have a data signal segment 6 instead of the blanking interval of the conventional television signal. The data signal segment 6 includes data pulse signals which contain in addition to sound information on line and field synchronization in coded form. This data segment 6 is followed by an analog color component segment 7 which is followed by an analog luminence component segment 8 as shown in FIG. 2. The MAC signals do not contain any analog synchronizing pulses or any black level with a timing relationship thereto and cannot, therefore, be displayed by usual conventional monitors since such monitors are not able to derive synchronizing information from the signals contained in the MAC signals. Up to this time, it is only been possible in the laboratory to display such MAC signals pictorially on the monitor using special techniques such as described in the publication Rundfunktechnische Mitteilungen year 1985, Vol. 1, Page 32, FIG. 14.